Electric, delay-type detonator assembly



March 16, 1965 A. BOSSARD ELECTRIC, DELAY-TYPE DETONATOR ASSEMBLY Filed June 26, 1961 FIGI FIG. 2

FIG. 3

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INVENTOR. ANDRE BOSSARD A TTORNEYS United States Patent nyme Frangaise, Rotten France, a corporation of France 7 Filed June 26, 1961, Ser. No. 119,463 Claims priority, application France, Jan. 13, 1961,

49,629 9 Claims. (or. 102-28) This invention relates to detonator or blasting-cap assemblies such as are used for detonating explosive charges in mining and similar blasting applications.

Principal objects of the invention are to provide detonators or blasting-caps which will be safer to use, especially in fire-damp and similar inflammable atmospheres, and will be more reliable in producing more uniform complete combustion of the explosive charge.

Conventional detonators may be arranged to introduce long delays (of the order of /2 second) or short delays about ten to twenty times shorter. In either case, a typical detonator assembly may comprise a copper tubular case having the main charge positioned at its lower end, a so-called initiator charge overlying the main charge, a copper perforate cap or cover over the initiator charge, and a relay tube overlying the cap and usually made of brass, and containing a small charge of delaying explosive composition. This relay tube is mounted with a tight fit in the tubular case, and is forced by axial compression into tight contact with the underlying perforate cap or cover.

In detonators of this and similar types, the cover which underlies the brass or the like relay tube must be capable of allowing the flame to pass from the relay charge to the initiating charge. Such an arrangement has a serious drawback in that the cover must then also pass the incandescent solid combustion products or slag which will be driven out of the relay tube on explosion of the detonator. Another serious drawback and source of hazard is that on the bursting of the detonator the relay tube will be crushed and broken up into fragmentts which are liable to be driven out into the surrounding atmosphere with consequent danger of igniting the same. This is especially true when the delaying charge used in the relay tube is such as to possess a slow-burning characteristic after compression. It has moreover been found that should a gap, even very small, be present between the delaying charge and the initiating charge, the delaying charge tends to break up at its lower end under the action of the heat evolved and of the pressure obtaining in the combustion chamber containing the igniter cap overlying the upper end of the delaying charge. When this occurs the flame is able to progress directly to the main charge, with an unpredictable reduction in the combustion time of the delay charge. Such a detonator consequently will lack fidelity and its operaton will be unreliable.

More specific objects of this invention are to eliminate the above-enumerated defects in the operation of conventional detonators. In the improved detonator according to the invention, the expulsion of incandescent slag from the delay charge or the relay tube itself into the inflammable surrounding atmosphere is positively pre vented, reducing the fire hazard. The partial by-passing of the relay tube by the flame is likewise prevented, providing more uniform detonator operation.

An electric blasting cap or detonator assembly according to the invention is chiefly characterized in that it includes two serially arranged relay members containing different delaying charges. That is, it includes a primary relay tube, e.g. of brass, with relatively thick walls and containing a primary delaying charge of such nature as 3,173,365 Patented Mar. 16, 1965 to retain its detonating characteristics on compression and producing solid slag, and a secondary relay member in the form of a centrally perforated disc of a malleable or ductile material, e.g. lead, having a bore diameter substantially smaller than that of the primary relay tube and containing a secondary delaying charge having a substantially higher combustion rate than the primary delay charge (e.g. from twice to ten times higher). The secondary delay charge is interposed between the primary delay charge and the usual perforate cap or cover overlying the initiating charge, which in turn overlies the main charge, and said secondary relay disc is axially forced against and into the primary relay tube so as to have an end of the secondary relay disc penetrate a cavity provided for that purpose within the primary relay tube, which cavity may be simply provided by failing to fill said primary relay tube to capacity.

The secondary relay disc may be metallic, e.g. lead, or made from other suitably malleable material, e.g. plastic.

The above and further objects, features and advantages of the invention will appear as the disclosure proceeds with reference to an exemplary embodiment shown in the accompanying drawings wherein:

FIG. 1 is an axial sectional view of a detonator according to the invention especially developed for mining blast work in the presence of fire-damp;

FIG. 2 is a separate view of the secondary relay member prior to its axial compression in the assembly; and

FIG. 3 is a similar view of the primary relay member prior to axial compression.

Referring especially to FIG. 1, an electric blasting cap or blasting detonator comprises a tubular case 1 made e.g. of press-formed copper sheet, having its lower end sealed by a unitary end wall and having its open upper end sealed with a plug 2 of plastic or other suitable material around which the wall of tubular case 1 is pressed or crimped as shown. The plug 2 is centrally perforated to receive electric conductor wires 3 which lead into a combustion chamber 16 provided in case 1 below plug 2. Mounted on the ends of wires 3 within chamber 16 is an igniter head or cap 4 of the conventional kind. Contained in the bottom of the case 1 is the main charge 5 and thereover is placed the usual perforate cover 8 in the shape of an inverted cup, made e.g. of copper sheet, having its flanges 6 force-fitted against the inner surface of the case 1, and containing an initiator charge 10. The transverse Web of the cover 8 is formed with a central aperture 9 to permit the passing of the flame from the overlying delay charges presently described.

In accordance with the invention, there is provided over the top of cover 8 a so-called secondary relay member comprising an initially cylindrical tubular disc 11 (see FIG. 2) of relatively soft or malleable material such as lead, formed with a central bore or aperture which is filled with a secondary delay charge comprising a small amount of very fast-burning powder 12. Over the washer 11 is positioned the primary relay member which may conventionally comprise an e.g. brass thickwalled tube 13 formed with a central bore 14. The central bore within the secondary relay member 11 is made substantially smaller than the central bore in primary relay member 13. Thus, one set of suitable dimensions is: diameter of bore in member 13 is .3 mm.; diameter of bore in member ll is .1 mm. The axial length of member 11 may vary e.g. from 1 to 5 mm.

It is important according to the invention that the primary delaying charge 15 in the primary relay member 13 should comprise a non-fusing powder composition, is. one that will retain detonating characteristics after compression, and also that it shall yield solid slag on combustion which slag shall not be discharged outward of the detonator by the pressure obtaining within chamber 16. On the other hand the secondary delaying charge in the secondary relay member 11 as stated must have a much higher combustion rate and hence must necessarily differ in composition from the primary delaying charge.

Moreover as shown in FIG. 3, when preparing the primary delay charge the tube 13 is incompletely filled so as to leave a gap 17 at its lower end, which may be about 1 or 2 mm. deep.

The assembly of the improved detonator may be effected as follows. The main charge 5 is first placed in the bottom of the case 1, then the initiator charge 18 and cap 8 are placed thereover. Over the perforate cap 8, the secondary relay unit 11-12 is positioned, followed by the primary relay unit 1345, with the gap 17 directed toward the secondary relay unit. The assembly so far obtained is then placed under a high axial pressure so that the secondary relay disc 11 made of lead, or other ductile or malleable material, is deformed and its upper end is partly forced into the gap 17, causing the material of the disc 11 within the gap 17 frictionally to engage the wall of the bore 14 in the tube 13. Simultaneously, the lower end of the disc 11 may normally assume a convex shape as shown in FIG. 1 in tight engagement with the end wall of the cap 8 which is complementarily deformed. This step is very important since it provides the intimate contact required according to the invention between the two delaying charges 12 and of the respective secondary and primary relay members, thereby ensuring smooth continuous combustion and uniform predictable combustion time. The assembly is then completed in the usual way to provide the complete detonator shown in FIG. 1.

Owing to the tightly interfitted relationship between the primary and secondary relay casings 13 and 11, the flame from the primary delay charge 15 is blocked off from the exterior together with the solid combustion products or slag therefrom, none of which will be discharged into the surrounding atmosphere on explosion of the detonator and bursting of the case 1. On the other hand, the extremely small secondary delay charge 12 (in an amount on the order of a few milligrams) within the secondary relay casing 11 is atomized by the explosion, instantly blowing out any sparks well before they can have ignited any fire-damp or other inflammable substance present in the surrounding atmosphere.

The arrangement of the invention makes it superfluous to provide any peripheral reinforcement or the like around the case 1 as has sometimes been done heretofore in such detonators in an attempt to prevent the brass relay casing 13 from being violently discharged out of the case 1 on explosion. As will be understood from the foregoing, this result is obtained according to the invention by the provision of a primary delay charge 15 retaining its detonating properties in compressed condition, associated with a secondary fast-burning delay charge 12 tightly interfitted with charge 15 so as to prevent separation of the two relay casings 111 and 13 on explosion.

Various modifications may be made in the single embodiment illustrated without departing from the scope of the invention.

What I claim is:

1. An electrical detonator, including an outer shell, a main charge disposed at one end therein, and an ignition means disposed at the other end therein; and, between said main charge and said ignition means and within said outer shell, there being arranged in consecutive serial order, in the direction from said one end to said other end, an initiator charge at least partly enclosed in a cap, a secondary relay member of relatively soft and malleable material having a bore filled with a secondary delay charge, the cover of said cap and a surface of said secondary relay member being in intimate, tight contact, said cover having a perforation aligned with the bore of said secondary relay member, and a primary relay member of relatively harder material having a bore filled with a primary delay charge of relatively slower burning rate than said secondary delay charge, said two bores'being in communication, and said two relay members being frictionally locked together.

2. The detonator of claim 1, wherein said secondary delay charge has a combustion rate of from substantially two to ten times said primary delay charge.

3. The detonator of claim 1, wherein said primary delay charge is of a type that retains its detonating properties under compression and produces solid combustion residue.

4. The detonator of claim 1, in which said bore of said primary relay member is substantially larger than that of said secondary relay member.

5. The detonator of claim 1, wherein a portion of said secondary relay member extends part way into and frictionally grips the bore of said primary relay member, whereby the two relay members are frictionally locked together.

6. The detonator of claim 5, wherein said portion is in intimate and tight frictional contact with the bore wall of said primary relay member.

7. The detonator of claim 6, wherein the bore of said primary relay member is substantially larger than that of said secondary relay member.

8. The detonator of claim 1, wherein said relatively soft material is lead.

9. The detonator of claim 1, wherein said relatively soft material is a plastic.

References Cited by the Examiner UNITED STATES PATENTS 2,863,392 12/58 Hill et al. 102-28 2,887,054 5/59 Bryan 102-28 2,942,513 6/60 Seavey et al. 86-1 2,960,932 11/60 Scherrer 102-28 2,968,985 1/61 Seavey 86-1 FOREIGN PATENTS 192,823 11/57 Austria.

199,551 9/58 Austria.

553,589 2/58 Canada.

728,262 4/55 Great Britain.

752,983 7/56 Great Britain.

SAMUEL F EINBERG, Primary Examiner.

ARTHUR M. HORTON, Examiner. 

1. AN ELECTRICAL DETONATOR, INCLUDING AN OUTER SHELL, A MAIN CHARGE DISPOSED AT ONE END THEREIN, AND AN IGNITION MEANS DISPOSED AT THE OTHER END THEREIN; AND, BETWEEN SAID MAIN CHARGE AND SAID IGNITIO MEANS AND WITHIN SAID OUTER SHELL, THERE BEING ARRANGED IN CONSECUTIVE SERIAL ORDER, IN THE DIRECTION FROM SAID ONE END TO SAID OTHER END, AN INITIATOR CHARGE AT LEAST PARTLY ENCLOSED IN A CAP, A SECONDARY RELAY MEMBER OF RELATIVELY SOFT AND MALLEABLE MATERIAL HAVING A BORE FILLED WITH A SECONDARY DELAY CHARGE, THE COVER OF SAID CAP AND A SURFACE OF SAID SECONDARY RELAY MEMBER BEING IN INTIMATE, TIGHT CONTACT, SAID COVER HAVING A PERFORATION ALIGNED WITH THE BORE OF SAID SECONDARY RELAY MEMBER, AND A PRIMARY RELAY MEMBER OF RELATIVELY HARDER MATERIAL HAVING A BORE FILLED WITH A PRIMARY DELAY CHARGE OF RELATIVELY SLOWER BURNING RATE THAN SAID SECONDARY DELAY CHARGE, SAID TWO BORES BEING IN COMMUNICATION, AND SAID TWO RELAY MEMBERS BEING FRICTIONALLY LOCKED TOGETHER. 